1. Field of the Invention
The invented apparatus is directed to an inflatable antenna system useful for the generation of plane electromagnetic waves. The invented apparatus can be used for compact ranges, and in other radar applications in which plane waves are required, or are beneficial.
2. Description of the Related Art
Compact ranges are radar installations that are used to test the radar signature of various aircraft, rockets, missiles or warheads (sometimes referred to as 'targets') to create data that can be used to identify such objects when encountered by radar in military operations, in commercial aviation, or in aerospace applications. The radar systems used in a compact range generate plane electromagnetic waves that simulate the character of radar-generated waves at relatively large distances from the radar source. Thus, rather than having to test a target for its signature at relatively large distances from a radar installation, the target can be positioned relatively near the plane-wave generating radar source, and the target will reflect the plane waves so as to generate signature data similar to that which would be obtained if the target were observed by radar at typical distances remote from the radar source. Because the target can be placed near the radar source in a compact range, testing of targets for their respective radar signatures is greatly simplified. Specifically, the target can be easily oriented on a stand in various attitudes for repeated signature testing. The compact range thus provides greatly simplified target testing compared to the alternative of positioning the target at a remote site, or actually testing the target in flight, which requires remote communications and cumbersome coordination of the activities of more than one person to repeatedly reorient the target in different attitudes for testing. Thus, the compact range greatly simplifies the compilation of signature data for targets.
At present, all compact ranges known to the inventor are dedicated facilities, that is, the facilities are built for the sole purpose of use as a compact range. Of course, if the dedicated facility is not used at all times for compact range testing, it could potentially serve other uses and thus avoid wasteful spending on additional facilities for uses that could be housed in one multi-purpose building or carried out in a single outdoor range. It would be desirable to overcome this disadvantage of previous compact range installations.
Also related to the present invention is the current state-of-the-art in inflatable radar antenna systems. Examples of such inflatable antenna systems are disclosed in U.S. Pat. No. 2,913,726 issued Nov. 17, 1959 to J. W. Currie et al., U.S. Pat. No. 3,005,987 issued Oct. 24, 1961 to K. M. Mack et al., U.S. Pat. No. 3,056,131 issued Sep. 25, 1962 to R. L. McCreary, U.S. Pat. No. 3,112,221 issued Nov. 26, 1963 to H. C. Price, U.S. Pat. No. 3,125,758 issued Mar. 17, 1964 to R. J. Koehler, U.S. Pat. No. 3,147,478 issued Sep. 1, 1964 to W. W. Bird, U.S. Pat. No. 3,413,645 issued Nov. 26, 1968 to R. J. Koehler, and U.S. Pat. No. 4,672,389 issued Jun. 9, 1987 to David N. Ulry. Nearly all of the above-identified inflatable antennas are designed for field deployment in military applications, and as such are provided with systems to protect the antennas and their feeds from extreme weather conditions. To this end, several of the inflatable antenna systems disclosed in these patents have inflatable housings which enclose the antenna and feed. While these antenna and feed housings are desirable for field deployment, they are not well-adapted for use in a compact range in which such housings are a hindrance and present undue complication in assembly, use and disassembly. Also, these antenna systems are supported by relatively complicated support devices, many of which have the capability of rotating the inflatable antenna structure to scan the generated radar pattern over an azimuth range. Although these support structures may be desirable in military field deployment situations, they are not well-suited for compact range applications. Furthermore, the antenna feeds of these radar systems are housed within the inflatable reflector structure or are attached thereto in a relatively complicated fashion which is necessary to protect the feeds and to assure that the feed is properly positioned and will work properly upon deployment with little or no time required for adjustment. Although such housing and positioning of the feed may be desirable in field deployment, it can be a hindrance to testing in a compact range application. In addition, although many of the above-mentioned inflatable antenna systems are designed for portability, they nonetheless require considerably more time, effort, and complication in assembly, use, and disassembly than is desirable in a compact range application. It would be desirable to overcome these disadvantages of previous inflatable radar antenna systems.